Commonly assigned U.S. Pat. No. 4,445,117, issued on Apr. 24, 1984, entitled "Transistorized Focal Plane Having Floating Gate Output Nodes", by Steven D. Gaalema and Michael D. Jack discloses a readout circuit having a source-follower-per-detector (SFD) configuration. The disclosed implementation requires that each unit cell of a radiation detecting array have four transistors, one of which is coupled to a reset clock (-RST) control signal input. Although this implementation provides a satisfactory solution for many applications there are some applications where it becomes necessary to significantly impact the design of a readout device in order to incorporate these features. As a result circuit performance and/or producibility may be adversely impacted. Specifically, it has been found necessary in order to accommodate the four transistor circuit disclosed in U.S. Pat. No. 4,445,117 to design Schottky infrared detector readout devices to include unit cell pairs comprised of unit cells that are mirror images of one another. However, the use of mirrored unit cells has also been found to cause a problem relating to odd/even signal nonuniformities, thereby adversely impacting readout performance. The odd/even signal nonuniformity is an artifact of the unit cell array layout and manifests itself as a detectable signal difference between unit cells disposed in odd and in even rows, and in odd and in even columns.
It is thus an object of the invention to improve on the four transistor unit cell SFD readout circuit by requiring only three transistors in each unit cell and by eliminating requirement for a reset clock.
It is a further object of the invention to provide a three transistor unit cell SFD readout circuit that beneficially eliminates odd/even nonuniformity problems encountered with Schottky readout arrays.